The present invention relates to ignition systems for internal combustion engines and in particular to a spark ignition system specifically adapted for two-cycle engines.
During the compression stroke in a two-cycle engine, a fresh fuel-air mixture is drawn into the crankcase and the spark plug is fired around the top dead center (TDC) position of the piston. On the power stroke, the fresh fuel-air mixture from the crankcase is forced into the combustion chamber and the exhaust gases from the previous combustion are accordingly forced out. This operation of expelling the exhaust gases from the combustion chamber is commonly referred to as scavenging.
Typically, the scavenging operation in two-cycle engines deteriorates during light loading and slow running operation to the extent that irregular combustions are likely to occur. More specifically, since a relatively small fuel-air mixture is being fed into a combustion chamber containing a relatively large quantity of burned gas, the fresh mixture is diluted with the residual gas so that the ignitability of the mixture is deteriorated. As a result, ignition will at times fail to take place, thus causing the engine to fire irregularly and operate in a rough manner.
Accordingly, it is the primary object of the present invention to provide an improved ignition system for a two-stroke internal combustion engine which increases the scavenging operation during low throttle operation of the engine.
In addition, it is an object of the present invention to provide an improved ignition system for a two-cycle engine that is adapted to ignite the spark plug in each cylinder only during every second compression stroke to increase the quantity of the fresh fuel-air mixture in the combustion chamber and thereby increase the scavenging operation during low throttle valve settings.
Furthermore, it is an object of the present invention to provide an improved ignition system for a two-cycle engine of the above-described type which eliminates the problem of misfiring during low throttle valve settings and insures that combustions occur at equal intervals, thus smoothing engine operation and enhancing drivability.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :